The present invention relates to a navigation system for use with a virtual colonoscopy. In particular, the present invention relates to a teniae coli derived coordinate system for guiding virtual colonoscopic navigation and for the registration of lesions in multiple scanned data sets.
Colorectal cancer, the second leading cause of cancer-related deaths per year in industrialized nations (e.g., see J. D. Potter, M. L. Slattery, R. M. Bostick, S. M. Gapstur, “Colon cancer: a review of the epidemiology,” Epidemiol Rev., vol. 15, no. 2, pp. 499-545, 1993), is an important public health concern. It may be prevented by early discovery and removal of precursor polyps. Optical colonoscopy is a widely-used procedure available to examine the colonic mucosa and is regarded as the gold standard for detection of colorectal polyps and cancer. However, the procedure is invasive, uncomfortable and requires intravenous sedation. Thus, screening recommendations are often ignored by the public. The introduction of a noninvasive or minimally invasive procedure for colonic evaluation should prove more widely appealing.
Virtual colonoscopy, also known as CT colonography (CTC), is a less invasive alternative to optical colonoscopy for examining the entire colon to detect polyps. This technique reconstructs a virtual endoscopic view within the colonic lumen from a cross-sectional imaging modality. In addition to conventional tomographic slice views, the virtual luminal navigation allows the observer to visualize normal and pathologic anatomy directly in three-dimensional (3D) spatial perception. Pickhardt et al. (Pickhardt, P. J. et al., The New England Journal of Medicine, 349(23):2191-2200 (2003)) have reported high sensitivity in detecting polyps using virtual colonic luminal fly-through navigation. The effectiveness of virtual endoscopic navigation in computer-aided diagnostic systems has received increasing recognition.
Most existing CTC protocols require a patient to be scanned in both supine and prone positions to increase sensitivity in detecting colonic polyps. As such, a reference system between scans becomes necessary. However, the conventional centerline approach (e.g., see Bitter, 1. et al., IEEE Transactions on Visualization and Computer Graphics, 7(3):195-206, (2001); Frimmel, H. et al., Proceedings SPIE Medical Imaging '03, SPIE 5031:381-387 (2003); Hong, L. et al., Proceedings SIGGRAPH '97, pp. 27-34 (1997); Iordanescu G. et al., Academic Radiology, 10: 1291-1301 (2003); Paik, D. S. et al., Med. Phys., 25(5):629-637 (1998)) generates only the longitudinal distance along the colon, which has a large variation and is less precise. Consequently centerline-based polyp registration requires colon length normalization (e.g., see Brickman, D. et al., Proceedings of RSNA Annual Meeting, p. 633, (2004); Li, P. et al., Med. Phys., 31(10):2912-2923, October (2004)). Besides, this approach also lacks the necessary orientation information to synchronize the virtual navigation cameras in both scanned positions. This makes the visual validation of polyp registration between scans a very time-consuming and a rather cumbersome task.
There is therefore a need for a virtual colonoscopy methodology that does not suffer from the above shortcomings.